In Short: A device for summing two or more electrical signals. In general audio usage, a device to process and sum the outputs of two or more microphones or line level sources

more detail:

A mixer is a piece of outboard equipment that mixes audio channels together. It can incorporate preamps to amplify mic levels to line levels, and sums them for output to a DAW, tape, or foldback/live mixes. To read more click below.

What is a mixer?
A mixer, or console, or recording mixer, or recording console, is essential for grouping and balancing incoming signals to be recorded or for live use.

It may be digital, analog, based inside a computer, or operated by switches, but the principles remain the same.

A common confusion in beginners is whether they need a mixer or an audio interface. In general terms, the former is for mixing analog tracks, and the latter is for taking analog tracks and converting them to digital for recording in a computer, where they can subsequently be mixed.

As ever in the fast-progressing world of pro audio, the lines are being blurred day-by-day. Modern mixers may feature onboard converters, firewire outputs and be able to perform as a true audio interface to a DAW. Equally, DAWs and audio interfaces are more and more able to output multiple channels for summing in a summing mixer or analog mixer.

For the purposes of discussion on this board, a mixer primarily is a console with preamplifiers built into each channel strip, faders, and buses for subgrouping and aux sends. An analog interface is primarily concerned with getting audio into a computer or DAW. Be aware of the differences.

Can I use a mixer to record with?

A basic mixer will sum together your input channels and produce a stereo output suitable for a PA. This output is also suitable for recording, but you will obviously be limited to 2 channel stereo, or 2 channels of mono. i.e. if you record the master output, you will have no further control over individual channels for mixing, panning and EQ.

Your mixer may have Direct Outs from each channel. If this is the case you will be able to record each of these channels to tape, hard disk recorder, or DAW.

However you will have 2 further factors to consider. The first is the quality of the preamps within the desk, which will dictate your overall recording quality.

The second factor is the number of input channels on your recording device:

Tape: The amount of tape tracks you have available to record to.

Hard-disk recorder: The amount of input channels your HDR has.

DAW: The amount of simultaneous recording, channels is not generally limited within a DAW but you will require A/D converters to convert the audio to digital. The amount of channels your audio interface or converter unit has will therefore be your limiting factor. These digitally converted channels will then be transferred via Firewire or USB to your DAW. Two further factors to consider are whether the bus speed of your interface method is high enough to support these channels (USB is much slower than Firewire and can be a limiting factor here) and the quality of the conversion itself which will again impact on your overall recording quality.

What goes on inside a mixer?

Gain Staging

Using a mixer is the first time we will go from our simple signal chain:

Mic > Preamp > A/D Converter > DAW

To a more complex one. Even in simple terms what goes on inside a mixer cannot be easily expressed in one line. Therefore we use flowcharts to discuss mixer functions. A more complex internal signal chain for a mixer might then look like this:

Input > Preamp > Channel Stage > PFL Bus > EQ > Fader > AFL Bus > 2-Bus > Output

Gain staging is the principle of matching the input and output levels of these stages to ensure maximal signal-to-noise ratio with minimal distortion.

I/O Modules

These are the channel strips which control each channel. The controls are duplicated over each module. Generally you will find a bare minimum of:

- XLR mic input
- mic gain or 'trim'
- balanced or unbalanced line input
- bus, aux and/or group routing and assignment
- EQ
- monitoring options
- solo and/or mute
- channel fader

Master or Centre Section

This section usually controls aux, bus and group send and return levels, levels of additional functions such as tape in/out via phono, mono in/out, routing of aux, bus, and/or groups, phones levels, and monitoring types and options.

Monitor Path

Larger "split consoles" may have another set of I/O modules after the centre section to deal with bus/group levels and tape return monitoring.